Rib flare is a postural condition where the lower ribs protrude outward and upward instead of sitting flat against the torso. It’s most visible at the bottom edge of the rib cage, along what’s called the costal margin, the cartilaginous border where your lowest ribs meet. You can often spot it by looking in a mirror: if the bottom edges of your rib cage visibly stick out, especially when you raise your arms overhead, that’s rib flare.
What Rib Flare Looks Like
The lower ribs are the ones involved. In a neutral rib cage, these ribs angle gently downward and tuck in toward your body. With rib flare, they’re pulled upward and push outward, creating a visible ridge or shelf beneath the chest. It can happen on one side (more commonly the left) or both. Some people also notice a dip or gap in the costal arch where the lower rib cartilage hasn’t fully formed or has shifted position.
One way clinicians assess rib position is by looking at the infrasternal angle, the V-shaped angle where the two sides of your rib cage meet at the bottom of the breastbone. A wider angle, generally over about 110 degrees, suggests the rib cage is in a more flared position. You can roughly gauge this yourself by placing your thumbs along the bottom edge of each side of your rib cage and seeing how wide that angle opens.
Why Ribs Flare Out
Rib flare has two broad categories of causes: structural and postural. On the structural side, it can occur alongside chest wall deformities like pectus excavatum (a sunken chest) or pectus carinatum (a protruding chest). In these cases, the flare is often the most noticeable part of the deformity, even when the underlying condition is mild. Rib flare can also exist entirely on its own, without any other chest wall abnormality.
The more common driver for most people is postural. It typically comes down to core weakness, poor breathing habits, or both. When your abdominal muscles aren’t strong enough to hold the rib cage in a neutral position, the lower ribs drift outward. This is often paired with an anterior pelvic tilt, where the pelvis tips forward, tightening the hip flexors and back extensors while weakening the abs, glutes, and hamstrings. That forward tilt pulls the torso into an exaggerated arch, pushing the lower ribs further out.
Poor sitting and standing posture compounds the problem. When the upper back (thoracic spine) is pushed into excessive extension, often from weak upper back muscles or habitual posture patterns, the rib cage flares open as a result.
The Connection to Breathing
Rib flare and breathing are tightly linked, and the relationship runs in both directions. When ribs are flared, the diaphragm, your primary breathing muscle, sits in a less effective position. Instead of descending fully into the abdominal cavity during an inhale, it’s already stretched and flattened. This pushes you toward shallow, chest-dominant breathing patterns where the upper chest and neck muscles do most of the work.
That shallow breathing triggers a cascade. Limited rib mobility interferes with your ability to take deep breaths, which can activate your body’s stress response. Your nervous system interprets the restricted movement as a threat and responds by tensing surrounding muscles as a protective mechanism. That tension further reduces how much your spine and ribs can move, especially during rotation and extension, creating a cycle that reinforces itself.
How Rib Flare Affects Your Body
The most common complaint tied to rib flare isn’t the visible protrusion itself. It’s lower back pain. When your rib cage becomes stiff and loses its ability to move well, your thoracic spine can’t rotate or extend the way it should. Your lumbar spine (lower back) picks up the slack, absorbing forces and movement demands it isn’t designed to handle long-term. Over time, this added strain often shows up as chronic tightness or pain in the lower back.
A stiff rib cage also limits upper body and mid-back movement more broadly. Your nervous system senses the instability and responds by creating protective tension, further restricting your range of motion. The result is an overall sense of tightness through the trunk that goes well beyond the ribs themselves.
Core function takes a hit too. When your ribs are flared, your abdominal muscles struggle to activate properly. The internal obliques, which play a key role in pulling the ribs downward and maintaining pressure in the trunk, lose their mechanical advantage. This means even people who exercise regularly can have poor core stability if their rib position is off.
Exercises That Help Correct Rib Flare
Correcting rib flare generally involves three things: retraining your breathing, strengthening your core, and improving mobility through the upper back and shoulders. These aren’t quick fixes, but they address the root causes rather than just the visible flare.
Breathing Retraining
Diaphragmatic breathing is the foundation. Lie on your back with one hand on your chest and one on your belly. Inhale slowly through your nose, directing the breath so your belly rises while your chest stays still. Exhale slowly through your mouth. The goal is to retrain your diaphragm to descend properly, which naturally pulls the lower ribs inward and downward. This also helps reduce chest-dominant breathing patterns and lowers the stress response that contributes to trunk tension.
Core Strengthening
The dead bug exercise is one of the most effective options. Lie on your back with your arms reaching toward the ceiling and your knees bent at 90 degrees. Slowly lower one leg and the opposite arm toward the floor, but stop the moment you feel your rib cage start to lift or flare. The key is keeping the lower ribs pointed toward your hips throughout the movement. A plank on your knees works similarly: hold the position while actively engaging your core and breathing normally, focusing on not letting the ribs splay open.
Mobility Work
Wall slides help improve shoulder and thoracic mobility without letting the ribs compensate. Stand with your back to a wall and slide your hands upward while consciously keeping your ribs pointed toward the floor. Overhead reaches with a stick follow the same principle: raise both arms overhead slowly and stop the moment you feel the ribs start to move. These exercises teach your body to move through the shoulders and upper back without defaulting to rib flare as a compensation.
The common thread across all of these is awareness of rib position. Most people with rib flare have spent years unconsciously letting their lower ribs drift outward. Correction starts with learning what a neutral rib cage feels like and cuing yourself to maintain it during exercise, standing, and sitting throughout the day.